1. Field of the Invention
The invention relates to bleach catalysts, compositions containing same and a method for using the catalysts for cleaning substrates, especially fabrics.
2. The Related Art
Many household and personal care products are formulated with an active oxygen-releasing material to effect removal of stain and soil. Oxygen-releasing materials have an important limitation; their activity is extremely temperature dependent. Temperatures in excess of 60.degree. C. are normally required to achieve any bleach effectiveness in an aqueous wash system. Especially for cleaning fabrics, high temperature operation is both economically and practically disadvantageous.
The art has partially solved the aforementioned problem through the use of activators. These activators, also known as bleach precursors, often appear in the form of carboxylic acid esters. In an aqueous liquor, anions of hydrogen peroxide react with the ester to generate the corresponding peroxyacid which oxidizes the stained substrate. Commercial application of this technology is found in certain fabric bleaching detergent powders incorporating sodium nonanoyloxybenzene sulfonate. This activator is typical of a class that features a phenol sulfonate leaving group; see U.S. Pat. No. 4,412,934 (Chung et al.).
While carboxylic acid ester activators and the like are often effective, they are not catalytic. Once the ester has been perhydrolyzed it can no longer be recycled. Therefore, relatively large amounts of activator are necessary. Amounts as high as 8% may be necessary in a detergent formulation for bleaching fabrics. Cost for these relatively expensive activators is of major concern at such levels.
A significant advance in catalysis was reported utilizing sulfonimines in U.S. Pat. No. 5,041,232, U.S. Pat. No. 5,047,163 and U.S. Pat. No. 5,045,223 all to Batal and Madison. Only a few of the reported compounds have been studied in any detail. More investigation needs to be conducted to identify catalysts of even greater activity.
Accordingly, it is an object of the present invention to provide novel bleach catalysts that can operate over a wide temperature range including that of under 60.degree. C.
It is another object of the present invention to provide bleach catalysts which are effective at relatively low concentrations thereby achieving a cost effective stain removal system.
A further object of the present invention is to provide a method for bleaching stained substrates such as clothes, household hard surfaces including sinks, toilets and the like, and even dentures.
Other objects of the present invention will become apparent through the following summary, detailed discussion and examples.